We investigated: 1) The effects of hyperinsulinemia on plasma and urinary levels of ET; 2) The effects of sodium intake on ET excretion (UETV) under normal conditions and in response to hyperinsulinemia; 3) The correlations between UETV and urinary sodium and flow. The euglycemic insulin clamp technique, developed by Dr. DeFronzo, was used, to assess the degree of insulin resistance and provide a controlled hyperinsulinemic state. So far we have studied only eleven normotensive subjects. Hyperinsulinemia increased urinary excretion of endothelin consistently but not significantly. The largest increase was observed in subjects on a high sodium diet. This effect was accompanied by significant increases in urinary flow. There were strong correlations between UETV and both urinary flow and urinary sodium. In contrast, neither insulin infusion nor changes in sodium intake significantly affected plasma levels of either ET or ANF.